This invention relates to a method of actuating hydraulic consumers by means of intrinsically-safe electro-hydraulic valves, and to an arrangement for controlling the actuation of such hydraulic consumers. In particular, the hydraulic consumers are hydraulic rams used in underground mining installations.
When winning coal in underground longwall mine workings, it is usual to use roof support units to support the roof. These support units include a plurality of hydraulic consumers, such as for example support props, advance rams and roof bar extension rams. The supply of pressurised hydraulic fluid to these consumers is usually controlled by means of electro-hydraulic valves.
Where electrically-actuatable hydraulic control valves are used in firedamp-endangered areas of underground mines, it must be ensured that no firedamp can be ignited by the energy supplied to the valves. The power consumption of such electro-hydraulic control systems is, therefore, correspondingly limited. These control systems have for example a current intensity of 1 to 1.5 amps for an operating voltage of 12 volts.
By reason of the high hydraulic pressure level usual in mining, the electro-hydraulic control valves usually used have a relatively high power consumption of up to 500 milliamps. With the support control systems used hitherto in underground workings, it is not possible to actuate a plurality of electro-hydraulic control valves at the same time. Such valves have to be actuated in sequence.
In the past various attempts have been made to overcome this disadvantage. For example, electro-magnetic valves are known which have a current consumption of about 125 milliamps with a voltage of 12 volts. However, these electro-magnetic valves have a relatively small flow cross-section, and consequently can permit the passage of only small quantities of liquid per unit of time.
A known electrically-actuatable hydraulic control valve has an electric drive mechanism which comprises an energy store in the form of a compression spring. The compression spring is initially compressed by means of a low-power electric geared motor, and liberates the energy stored in the compression spring suddenly for the opening of the valve. (See DE-OS No. 3 123 224).
The aim of the invention is to provide a method of, and an apparatus for, controlling the simultaneous actuation of a plurality of hydraulic consumers in use in a firedamp-endangered surrounding.